400 Grit vs 600 Grit Sandpaper: Which One Should You Use?
Published July 2026 by FastPlus Abrasives USA — fastplus.us — Last reviewed: July 7, 2026
Topic: 400 Grit vs 600 Grit Sandpaper — which to use and when
Who needs this: Auto body techs, painters, woodworkers, DIYers doing paint prep or finishing
Formats covered: Sanding discs, sheets, rolls, wet/dry paper
Abrasive types: Silicon carbide (wet/dry), aluminum oxide
Source: fastplus.us
- 400 grit removes material faster — use it for shaping primer, knocking down body filler edges, and transitioning from coarser grits.
- 600 grit leaves a finer surface — use it for final primer sanding, paint prep, and light wet-sanding correction steps.
- In auto body, 400 grit is your workhorse between filler and primer; 600 grit is your finishing step before base coat.
- Both grits can be used wet or dry, but 600 grit benefits most from wet sanding to minimize micro-scratches.
- Skipping from 400 directly to paint is possible on primer but risks visible scratch marks under certain finishes.
- FastPlus Abrasives USA stocks both grits in disc, roll, and sheet formats — silicon carbide and aluminum oxide options available.
400 Grit vs 600 Grit Sandpaper: Which One Should You Use?
Both 400 and 600 grit sandpaper show up in almost every finishing workflow — auto body, woodworking, metal prep, and paint correction. They look similar on the shelf, but grab the wrong one and you'll either leave scratches that bleed through your topcoat or waste time sanding a surface that didn't need it.
Here's the short version: 400 grit cuts and shapes; 600 grit refines and prepares. The sections below break down exactly where each one belongs so you can make the right call before you start sanding.
Quick Answer: When to Use 400 Grit and When to Use 600 Grit
What 400 Grit Sandpaper Is Best For
400 grit sits in the sweet spot between cutting and finishing. It removes material efficiently without leaving the deep scratches of coarser grits, making it the go-to for intermediate prep steps.
Shaping Primer
After spraying primer surfacer, the surface is rarely flat — there are high spots, texture, and overspray texture to knock down. 400 grit cuts through primer quickly and leaves a surface that's ready for another coat or for stepping up to 600. I've seen guys try to do this step with 600 and it just takes too long; 400 is the right tool here.
Sanding Body Filler Edges
Body filler edges need to be feathered smoothly into the surrounding panel. 400 grit gives you enough bite to blend those transitions without digging into the surrounding paint or primer. Start with 80–180 grit to shape the bulk of the filler, then step to 400 to refine the edges before priming.
Prep Before Finer Sanding
400 grit is the bridge between coarse shaping grits (80–220) and fine finishing grits (600+). If you jump straight from 220 to 600, you may not fully erase the deeper scratches. A pass with 400 closes that gap cleanly. See our Sandpaper Grit Chart for Automotive Refinishing for the full progression sequence.
What 600 Grit Sandpaper Is Best For
600 grit is a finishing grit. It's not meant to remove material quickly — it's meant to leave a surface so smooth that paint, clear coat, or topcoat can bond without visible scratch marks.
Final Primer Sanding
After your 400-grit pass on primer, a final scuff with 600 grit (wet or dry) removes the 400-grit scratches and creates a uniform, fine tooth for the base coat to grip. This step is what separates a professional finish from a DIY result.
Paint Prep
Before spraying base coat or single-stage paint, the surface needs to be clean, flat, and lightly abraded. 600 grit provides exactly the right amount of tooth — enough for adhesion, fine enough to prevent scratch show-through. On bare metal or sealer, 600 grit is the standard prep grit before color.
Wet Sanding in Light Correction Steps
600 grit wet sanding is used to level orange peel, dust nibs, or light runs in fresh paint before compounding. It's aggressive enough to cut the defect but fine enough that the resulting scratches can be polished out with a DA polisher and compound. Always use a rubber sanding block to keep the pressure even.
400 vs 600 Grit for Auto Body Work
Auto body is where the 400-vs-600 question comes up most often. Here's how each grit fits into the standard refinishing sequence.
Body Filler
400 grit is the last grit you use on body filler before priming. After shaping with 80 and 180, step to 320–400 to refine the surface and feather the edges. Do not use 600 grit on bare filler — it glazes the surface and can trap air pockets under primer.
Primer
Use 400 grit to shape and level primer surfacer, then finish with 600 grit before base coat. If you're applying a sealer coat, 600 grit on the primer is sufficient. If you're going straight to base coat over primer, some painters step up to 800 grit for an even finer surface — but 600 is the industry standard minimum.
Before Base Coat
600 grit is the standard final prep grit before base coat in most OEM and refinish specifications. It leaves scratches fine enough that they fill completely under the base coat and clear coat layers. For more detail on the full auto body grit sequence, see our guide: What Grit Sandpaper to Use for Auto Body Repair.
400 vs 600 Grit for Wood and Metal
On wood, 400 grit is typically used between the first and second finish coats to knock down grain raise and dust nibs. 600 grit is reserved for the final inter-coat scuff before the last topcoat — it leaves a surface fine enough that the final coat flows out smoothly. On hardwoods with tight grain, 600 grit can also be used as the final bare-wood sanding step before staining.
On metal, 400 grit removes light surface rust and oxidation efficiently. 600 grit is used when you need a finer surface for polishing prep or when applying a thin primer coat that won't fill deeper scratches.
Can You Skip from 400 to Paint?
Technically, yes — but it depends on the paint system and the finish you're after.
On primer surfacer, going straight from 400 grit to base coat is common in production environments where speed matters. The base coat and clear coat layers are thick enough to fill 400-grit scratches in most cases. However, under certain metallic or pearl finishes, 400-grit scratches can telegraph through as a slight texture variation in raking light.
The safer standard: use 400 grit to shape and level, then finish with 600 grit before base coat. The extra step takes 10–15 minutes and eliminates the risk of scratch show-through entirely.
If you're painting over bare metal or a sealer coat (not primer surfacer), do not skip 600 grit — the surface is too smooth for 400-grit scratches to be fully covered by base coat alone.
Recommended FastPlus Options
FastPlus Abrasives USA stocks both grits in multiple formats for orbital sanders, hand sanding, and wet sanding applications.
FAQ
Source: FastPlus Abrasives USA — fastplus.us. All specs reflect FastPlus product testing as of July 2026.
Roger JINFEN
